The present invention concerns a rock cistern or tunnel with a tightly sealing lining for the inner surface of its wall structure and its supporting structure consisting of a steel-reinforced, water-tight sprayed concrete layer.
It is well-known practice to use caverns blasted in rock for storing various liquids and gases, without lining. In these cases the products to be stored are immiscible with water and lighter than water. That such liquids and gases are held in storage is based on the pressure of the water surrounding the rock cavern being higher than that of the product to be stored has. This has however the consequence that ground water flows into the place of storage. On the other hand, if the storing pressure of the liquid or gas is high, one is compelled to excavate unreasonably deep caverns, and this involves high costs. In cases in which no water contact of the product to be stored is permitted, lining of the storage walls is indispensable.
As to the state of art, reference is made to the European patent application No. 79101881.5 (publicizing No. 0007413), in which against the blasted rock surface there is a first concrete layer and against the inner surface of the wall structure, a second concrete layer. There is a protective layer and a tightly sealing film between these layers. A drawback of this kind of wall structure is that no anchors can be carried through said film. In addition, the percolating water collects between the first concrete layer and the film.
In the British Pat. No. 1,574,367 is disclosed a rock cistern wall structure of which the inner surface is a lining. This wall structure is composed of structural concrete elements to which the steel lining has been concreted fast. The design requires that there is an empty space for percolating water between the element and the blasted rock surface. This wall structure of the prior art is embarrassed by the drawback that the construction is extremely costly. Resistance against high inside pressure requires the use of thick steel sheet, which increases the price of the wall structure. A further drawback is its susceptibility to corrosion damage because the anchoring members have been carried through an empty space.
It is known in the art to coat the rock wall with sprayed concrete and to seal such a lining with plastic coatings. However, the successful applying of the methods of the prior art has been inhibited by the fact that the groundwater forces its way through the sprayed concrete lining and prevents adherence of the lining, and detaches the coating during use. Endeavors have been made to eliminate this by means of subdrains provided behind the sprayed concrete lining, which have the task to carry the harmful percolating water to a drain. Since the water only moves in fissures in the rock and such fissures are often highly abundant, the requisite drains would be so numerous that the required fixing of the concrete lining to the rock could no longer be provided.